RFC: How to decide which backend(s) to use

[keith preston]

This is a really difficult question.   One that I didn't know how to do.
Originally, I had planned on accuracy as the defining point.    Each backend
would signal a master process about it's accuracy and when it got more
accurate.   From this the clients would chnge over to the more accurate
backends.


I thought this would suffice, but the civic location idea does bring up
problems.   What if different backends implement different methods?   I
still vote for allowing more control from the programmers, but maybe
providing examples on how to change between providers and such.

Keith Preston


On 6/19/07, Jussi Kukkonen <jhkukkon at cc.hut.fi> wrote:
>
> This RFC is actually somewhat related to the earlier (hopefully even
> ongoing) discussion on interfaces.
>
>
> Selecting the backend to use is not just a matter of choosing the
> default one, if we want to do it right. Example: Let's say the user has
> the following position backends installed
>    1. GPS
>    2. Hostip
>
> Scenario 1. Application wants to know the city/country (assume civic
>             location is now included in the position-interface).
> Scenario 2: An application wants coordinates. User does not have a GPS
>             device with her (or she is indoors).
>
> In both scenarios the default GPS backend is unusable. Problem in
> scenario 1 is something that could be avoided with having separate
> interfaces for civic/coordinate location, but that is just a special
> case. Scenario 2, and many other situations like it, would require the
> application to call get_all_position_providers() and try another backend
> if the current_position()-method of the first backend failed... This is
> not friendly at all.
>
>
> Conclusions/questions:
>
> * There should be an order of preference for backends
>   (a list in gconf instead of just the default backend?)
>
> * Getting information from the several backends should be as seamless as
>   possible. I don't see why we couldn't totally abstract this in the
>   bindings / wrapper library?
>      If a method (e.g. current_position()) fails, and
>      if no backend was initialized with generic init-method and
>      if there are backends still left on the list of backends
>           Initialize the next backend in the list and
>           call the current_position method() on the new backend
>
> Is there something seriously wrong with this idea? If it works,
> applications could just say
> "I want [Coordinates|City Name|Street Address|...]"
> and get that information without knowing any details.
>
>
>   -jussi
>
>
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